Event detection system

ABSTRACT

An event detection system ( 100 ) comprises: a communication network of interconnected nodes ( 10 ) and a central control station ( 200 ), each node being capable of communicating to at least one adjacent node and/or to the central control station, each node comprising: at least one microphone ( 11 ); a GPS receiver ( 12, 13 ) providing information regarding its location and providing time information; a processing circuit ( 17 ), capable of processing the microphone signals, the processing circuit being designed to detect the occurrence of predetermined characteristic sound patterns, and if the occurrence of a predetermined characteristic sound pattern is detected, to communicate the detected event to the central station, together with information regarding location of the node and time of detection; wherein the central station is designed to process the information received from the nodes and to determine the location of the audio source and the occurrence time of the event.

The present invention relates in general to an event detection system.

In the context of the present invention, events to be detected areevents such as car accidents, airplanes flying over at low altitude, aburglar breaking into a home, etc. It is desirable to detect theoccurrence of such events, and to take appropriate action in response.For instance, in residential areas, low-flying airplanes may bedangerous and hence forbidden, and the accompanying noise may beannoying to people, who wish to complain, but it is very difficult forsuch people to determine the exact altitude and trajectory of the plane.In case of breaking and entry, it is very desirable to respondimmediately. In case of a car accident, it is desirable to directemergency personnel to the accident location as quickly as possible, andto arrange for the traffic to be directed away from the accidentlocation. Important minutes may go by in case the officials wait until abystander calls for emergency assistance by telephone. Further, in theaftermath of a car accident, legal issues may arise: how fast did thecar(s) drive, did the parties use their brakes, etc. The answers tothese questions may have influence on the question of who is responsibleand has to pay the damages.

Thus, an important objective of the present invention is to provide anevent detection system capable of reliably detecting not only theoccurrence of such events, but also the event location, and time ofoccurrence.

According to an important aspect of the present invention, an eventdetection system comprises a communication network of interconnectednodes, each node being capable of communicating to at least one adjacentnode and/or to a central control station. Each node comprises at leastone microphone arranged outdoors, or at least arranged such that outdoorsound can freely reach the microphone. Each node further has informationregarding its location; in a preferred embodiment, each node comprises aGPS receiver receiving signals from the satellites of the well-known GPSsystem, providing position information. Further, all nodes areassociated with accurately synchronised clock means; in a preferredembodiment, each node comprises a GPS receiver receiving signals fromthe satellites of the well-known GPS system, providing accurate timeinformation.

The nodes are preferably arranged in an array at mutual distances in theorder of 10-100 m. In a very suitable embodiment, the nodes areassociated with street lighting armatures or lamp posts, of which themutual distance in practice typically is in the order of about 30 m.Communication between nodes may occur by any suitable means, wired orwireless, for instance by telephone but preferably communication takesplace over optical links.

Each node comprises a sound processing circuit, capable of processingthe output signals of the corresponding microphone, and designed todetect the occurrence of predetermined characteristic sound patterns.For instance, a car collision produces sound with a very characteristicsound, which, with suitable sound processing, can easily bedistinguished from normal traffic noise. Likewise, the screeching noiseof a car with blocked wheels desperately trying to make an emergencystop can easily be distinguished from normal traffic noise. Even theexplosion of an air bag produces sound with a very characteristic sound,which can easily be distinguished from normal traffic noise. Likewise,the sound of breaking glass can easily be distinguished.

A first part of sound processing is executed by the sound processingcircuits of the nodes. Thus, each node is capable of determining whetherone or more of predetermined events occur in its surroundings, orbetter: within its sound detection field. If so, the event detected iscommunicated to the central station, together with information regardinglocation of the node and time of detection.

The central location receives input from a plurality of nodes, thenumber depending on the loudness of the sound. By comparing the timinginformation contained in its input signals, the central location iscapable of determining quite accurately the location of the audiosource, its direction of travel, etc. Further, the central location iscapable of determining quite accurately the occurrence time of theevent.

In a preferred embodiment, each node comprises a buffer for storing apredetermined amount of input signal, for instance 30 seconds of ambientsound. Then it is possible, if an event occurs, to store the sound ofthe period immediately before the event, for later analysis.

These and other aspects, features and advantages of the presentinvention will be further explained by the following description withreference to the drawings, in which same reference numerals indicatesame or similar parts, and in which:

FIG. 1 schematically shows a top view of a traffic situation at a streetcrossing;

FIG. 2 is a block diagram schematically illustrating elements of a node;

FIG. 3 is a graph schematically illustrating sound picked up by a node.

FIG. 1 schematically shows a top view of a street crossing 1, where aside street 2 crosses a main street 3. The streets 2, 3 are providedwith street lighting armatures 6, mounted on lighting poles not shownfor the sake of clarity. Each lighting armatures 6 is provided with anode 10 of an event detection system 100 according to the presentinvention. These nodes 10 cooperate to process and recognize the outdoorsound. As shown in FIG. 2, each node 10 comprises a microphone 11, whichis mounted such that it can receive outdoor sound. Each node 2 furthercomprises a sound processing circuit 17, having an input coupled toreceive the output signal of the microphone 11. The sound processingcircuit 17 is capable of processing the output signals of thecorresponding microphone 11; more particularly the sound processingcircuit is designed to detect the occurrence of predeterminedcharacteristic sound patterns.

The event detection system 100 further comprises a central station 200which, in the embodiment as shown in FIG. 1, is associated with one ofthe nodes 10. All nodes are capable of communicating with this centralstation 200, either directly or indirectly, through other nodes.

Each node further comprises a signal buffer 16, having an architectureof a shift memory (first in first out), and having a capacity to storethe equivalent of about 30 sec of the signal of the microphone 11. Itshould be clear that the size of the signal buffer 16 may be larger orsmaller than 30 sec.

Each node 10 further comprises location means 12 arranged for providinginformation regarding the location of the node 10. This location means12 may be a simple memory, in which the location coordinates are storedby the manufacturer, or by personnel on mounting the node 10 in place.Preferably, however, the location means 12 comprises a GPS receiver, asindicated, receiving GPS signals from the satellites of the OPS system.Since the GPS system is well-known to a person skilled in the art, it isnot necessary here to explain this system in more detail; suffice it torecall that the GPS signals allow a suitable designed receiver tocalculate the coordinates of its location.

Each node 10 further comprises clock means 13 arranged for providinginformation regarding the date and the local time of days. This clockmeans 13 may, in principle, be any common clock signal generator, havingsufficient accuracy, but the clock signals of all clock means of allnodes should be synchronised. Preferably, the clock means 13 comprise aclock receiver, receiving a common clock signal, for instance generatedby the central station 200. In a most preferred embodiment, the clockmeans 13 comprises a GPS receiver, as indicated, receiving GPS signalsfrom the satellites of the GPS system. Since the GPS system iswell-known to a person skilled in the art, it is not necessary here toexplain this system in more detail; suffice it to recall that the GPScontains accurate timing information.

A first car A travels on the main street 3; a second car B approaches onthe side street 2. When A sees B, he tries to break, causing break marks4 with his wheels being blocked, but it is too late: a collision occurs.The collision causes sound waves, indicated at W, which sound waves arepicked up by the microphones 11 of the nodes 10. The sound caused by acollision has a very characteristic sound pattern, which is recognizedby the sound processing circuits 17 of the nodes 10, so that the soundprocessing circuits 17 decide that an event “collision” has occurred.

In response to detecting the occurrence of a collision (or other event),each sound processing circuit 17 is programmed to notify this event tothe central station 200. In its communication to the central station200, the sound processing circuit 17 includes information regarding thelocation of the corresponding node 10, and information regarding thetime of occurrence of the event. In this respect it is noted that eachnode may have received a unique identification number (ID); if thecentral station 200 comprises a memory (for instance a table) relatingthe node IDs to their respective locations, the sound processing circuit17 may simply communicate its ID to the central station 200, and thelocation means 12 may merely comprise a small memory containing the nodeID.

As should be clear to a person skilled in the art, the nodes closer tothe place of the collision receive the characteristic sound patternearlier than nodes located farther away. Thus, by comparing location andtime information contained in the incoming signals from the nodes, thecentral station 200 is capable to calculate the exact time and locationof the event.

In such calculation, the central station 200 will take into account thepropagation speed of sound waves in air (sound speed). Thus, propagationtime of a sound wave corresponds to length of propagation path. In afirst approximation, it may be assumed that the sound speed has the samevalue at all locations and in all directions, this value being a knownvalue (about 300 m/s). Then, the sound waves W will have circular shapescentred at the event location, as illustrated in FIG. 1. Calculating apoint of origin of the sound is relatively easy then, as will beappreciated by a person skilled in the art. However, in practice it mayturn out that the sound speed is not as homogeneously distributed over awide area. Propagation speed may be influenced by wind speed, which canbe visualised as a deformation of the shape of the sound waves. Also,objects such as buildings may force sound waves to take a detour, alsoeffectively causing deformations of the sound waves. Such effects mayaffect the accuracy with which the central station 200 is capable ofcalculating the event location.

In a preferred embodiment, the event detection system of the presentinvention is capable of compensating for these effects. Moreparticularly, the system may be provided with measuring means capable ofgenerating signals to the central station 200 indicating sound speed.

In one embodiment, one or more of the nodes 10, preferably all nodes,comprise a wind sensor 22, i.e. a sensor capable of generating a signalindicative of wind direction and wind speed. Since such wind sensors areknown per se, it is not necessary here to explain its design andfunctioning in more detail.

The nodes 10 may be designed to regularly or even constantly send windspeed and wind direction information to the central station 200.However, this is not necessary. Usually, it suffices if a node, whendetecting an event and notifying this to the central station 200, alsoincludes wind speed and wind direction information.

It should be clear to a person skilled in the art that the centralstation 200, when having information regarding wind speed and winddirection at a large number of locations, preferably corresponding tothe locations of the nodes, is capable to take this information intoaccount when calculating the location of the event.

It is noted that the system may also, additionally or alternatively,comprise one or more wind sensors not mounted to a node, yet capable ofcommunicating wind information to the central station 200, for instancevia a node.

In another embodiment, one or more of the nodes 10, preferably allnodes, comprise a loudspeaker 31 capable of generating a pilot tone. Onreceiving a certain instruction from the central station 200, a speakercontroller 30 of a node may drive the corresponding loudspeaker 31 toemit a sound having a predetermined duration and spectrum (for instance,having substantially only one predetermined tone or combination oftones). This sound will be picked up by the microphones 11 ofsurrounding nodes, who will communicate this fact to the central station200, together with the time of receipt. It is also possible that suchspeaker controllers 30, more or less autonomously, drive thecorresponding loudspeaker 31 to emit the pilot sound, coded such as tocontain time and location (node ID) of transmission. In both cases, thecentral station 200 will have at its disposal information regarding timeand location of transmission and information regarding time and locationof receipt, so for each combination of transmitting node A and receivingnode B, the central station 200 is capable to calculate the propagationtime, i.e. the time needed for a signal to travel from A to B.Especially if the central station 200 also receives information allowingit to calculate the time needed for a signal to travel from B to A, thecentral station 200 is capable of calculating wind speed between A andB. Based on such propagation time measurements and/or wind speedmeasurements, the central station 200 can more accurately calculateevent location, as should be appreciated by a person skilled in the art.

It is noted that the system may also, additionally or alternatively,comprise one or more pilot tone generators not mounted to a node, yetcapable of communicating to the central station 200, for instance via anode.

FIG. 3 is a graph schematically illustrating, by way of example, thesound pattern S (vertical axis) received by a node 10A as a function oftime (horizontal axis). At time t0, the sound processing circuit 17 ofthis node detects the characteristic sound pattern of a car collision.The time interval from t0-M to t0 corresponds to the signals currentlypresent in the signal buffer 16. These signals may represent the car Apassing node 10A at time t1, and starting to brake at time t2. In thepreferred embodiment where the nodes 10 are provided with a signalbuffer 16 as mentioned, each sound processing circuit 17 is programmed,in response to detecting the occurrence of a collision (or other event),to also communicate to the central station 200 the contents of itssignal buffer 16. Using the contents of the signal buffers of severalnodes, the central station 200 is capable, for instance, to calculatewhen and where the cars started to brake, an to calculate how fast eachcar was driving immediately before the drivers hit the brake.

The central station 200 may be programmed to passively wait for thenodes 10 to send data. Preferably, however, the central station 200 iscapable to send commands to individual nodes, causing such nodes tocommunicate to the central station 200 the contents of their signalbuffers 16. So, even if a node has not detected an event, the contentsof the signal buffer 16 of such node may be used by the central station200. Thus, depending on the size of the signal buffer 16, it is possibleto track the car A further back in history as regards its location,hence its speed.

Immediately after the event has occurred, the central station 200 isaware of this, and also the central station 200 knows the location ofthe event and the nature of the event. The central station 200 may bedesigned to take action, such as by sending a call to rescue services,police, etc.

In a preferred embodiment, one ore more of the nodes, preferably eachnode 10, is also provided with a video camera 14, capable of takingvideo pictures from the scene in its surroundings, in which case theprocessing circuit 17 may be programmed to send to video signals to thecentral station 200. The video camera 14 may be constantly active, butit is also possible that the video camera 14 is only activated by thecentral station 200 as action in response to detecting an event. Thus,it is assured that only those cameras in the vicinity of an eventlocation are operative.

With such camera pictures at their disposal, control personnel iscapable to quickly assess the situation and, if necessary, to takefurther action. It is also possible that the central station 200 hasvideo processing capabilities, for automated situation assessment andaction. Further action may involve controlling traffic lights. Forinstance, in the situation depicted in FIG. 1, assume that the crossingis provided with traffic lights: in order to prevent a traffic chaos,the central station 200 may set all traffic light to red, except thelights for the road where rescue services are expected to approach thescene, so that traffic is allowed to evacuate the road for the rescueservices and allow them free access. Such action may be automatic, butmay also be taken by surveillance personnel.

On the other hand, in preferred embodiments where nodes comprise videocameras, such cameras may be constantly operative. The processing device17 may be provided with image processing software in order to detect theoccurrence of events, such as speeding, ignoring red traffic lights, orpossible criminal activity. If such events are detected, the centralstation 200 is notified, and one or more video images are sent to thecentral station 200, where they are stored as evidence. It is noted thatconventional traffic cameras need photographic films, which need to beentered into the camera, taken away after some time, developed, etc.

Image processing software also allows a processing device 17 to “read”registration plates. The central station 200 may issue a communicationto all nodes 10 that a certain car having a certain registration platehas been stolen. Each processing device 17 stores this information in anaccompanying memory. The processing device 17 processes the images fromthe camera 14, recognizes a car, recognizes the registration plate ofthe car, and recognizes the registration number of the registrationplate. The processing device 17 compares this registration number withthe information in its memory. In case of a match, the processing device17 determines that an event is taking place, i.e. a stolen car ispassing, and sends a communication to the central station 200. The imageprocessing software of the processing device 17 allows the speed anddirection of the stolen car to be determined. Adjacent nodes may be“warned” to be extra alert for this registration number, so thatdetection by adjacent nodes is accelerated.

Preferably, one or more of the nodes 10, more preferably each node 10,further comprises a weather detector and/or a seismic detector 24. Forinstance, a weather detector may comprise a temperature sensor 21, awind sensor 22, a rain sensor 23, etc.

The readings from sensors 21, 22, 23 may be continuously or regularlycommunicated to the central station 200, so that the system as a wholeconstitutes a fine-mazed weather station, which may also includebarometric sensors, humidity sensors, etc. The processing circuit 17 mayalso be designed to monitor the weather sensors 21, 22, 23 for eventswhich may have an influence on traffic safety, such as heavy rain, heavywind, freezing cold temperatures, etc. If such events are detected, theprocessing circuit 17 may communicate such to the central station 200,which may arrange for a public warning to be issued, for instance overthe radio, so that car drivers may hear this warning on their car radio.It is also possible that cars are equipped with communication devicesallowing them to communicate directly with the nodes 10, in which casethe nodes may send the weather information to a car directly. Inresponse, a control device onboard of such car may automatically switchON or OFF apparatus like heating equipment, airconditioning equipment,windscreen wipers, etc.

Conversely, modern cars may have one or more weather sensors, forinstance a rain sensor, a temperature sensor, etc. Cars may be equippedwith communication devices allowing them to communicate directly withthe nodes 10, in which case the cars may communicate the readings oftheir weather sensors to the nodes.

It should be clear to a person skilled in the art that the presentinvention is not limited to the exemplary embodiments discussed above,but that several variations and modifications are possible within theprotective scope of the invention as defined in the appending claims.

In the above, the present invention has been explained with reference toblock diagrams, which illustrate functional blocks of the deviceaccording to the present invention. It is to be understood that one ormore of these functional blocks may be implemented in hardware, wherethe function of such functional block is performed by individualhardware components, but it is also possible that one or more of thesefunctional blocks are implemented in software, so that the function ofsuch functional block is performed by one or more program lines of acomputer program or a programmable device such as a microprocessor,microcontroller, digital signal processor, etc.

1. Event detection system (100), comprising: a communication network of interconnected and cooperating nodes (10) and a central control station (200), each node being capable of communicating to at least one adjacent node and/or to the central control station, each node comprising: at least one microphone (11) arranged for receiving outdoor sound; location means (12) providing information regarding its location; clock means (13) providing time information; a processing circuit (17), capable of processing the output signals of the corresponding microphone (11), the processing circuit (17) being designed to detect the occurrence of predetermined characteristic sound patterns, and if the occurrence of a predetermined characteristic sound pattern is detected, to communicate the detected event to the central station (200), together with information regarding location of the node and time of detection; wherein the clock means (13) of all nodes are accurately synchronised; and wherein the central station (200) is designed to process the information received from a plurality of nodes and to determine the location of the event and the occurrence time of the event.
 2. System according to claim 1, wherein each node comprises a GPS receiver (12, 13) receiving GPS signals, containing accurate position information and accurate time information.
 3. System according to claim 1, wherein the central station (200) is designed, when calculating the location of the event, to take into account the propagation speed of sound waves.
 4. System according to claim 3, wherein the propagation speed of sound waves is taken to be constant.
 5. System according to claim 3, wherein the central station (200) is designed to compensate for deviations of propagation speed.
 6. System according to claim 5, further comprising at least one wind sensor (22) capable of generating a signal indicative of wind direction and wind speed.
 7. System according to claim 5, further comprising at least one loudspeaker (31) capable of generating a pilot tone.
 8. System according to claim 1, wherein the nodes are arranged in an array at mutual distances in the order of 10-100 m.
 9. System according to claim 1, wherein the nodes are associated with street lighting armatures (6) or lamp posts.
 10. System according to claim 1, wherein the nodes are designed for communication over optical links.
 11. System according to claim 1, wherein each node comprises a buffer (16) having a size sufficient for storing a predetermined amount of input signal, for instance corresponding to 30 seconds of sound.
 12. System according to claim 1, wherein each node further comprises a video camera (14).
 13. System according to claim 12, wherein the video camera (14) of a node (10) is activated by the central station (200) in response to detecting an event.
 14. System according to claim 12, wherein the processing device (17) is provided with image processing software.
 15. System according to claim 14, wherein the image processing software is capable to recognize events such as, for example, speeding, ignoring red traffic lights, or possible criminal activity.
 16. System according to claim 14, wherein the image processing software is capable to read registration plates.
 17. System according to claim 15 or 16, wherein the processing device (17) is designed to send one or more video images to the central station (200).
 18. System according to claim 16, wherein the central station (200) is designed to communicate wanted registration numbers to the nodes (10), and wherein the processing devices (17) are designed to compare a registration number of a camera image with the wanted registration numbers.
 19. System according to claim 1, the nodes (10) further comprising at least one sensor from the group comprising a temperature sensor (21), a wind sensor (22), a rain sensor (23), a seismic detector (24), a barometric sensor, a humidity sensor.
 20. System according to claim 19, wherein the processing circuit (17) is designed to monitor the said sensors for events which may have an influence on traffic safety, and to communicate such event to the central station.
 21. System according to claim 1, wherein the nodes are adapted for communication with individual cars.
 22. System according to claim 21, wherein the nodes are designed to communicate weather information to the passing cars.
 23. Vehicle, adapted for communication with a node of a system of claim
 1. 24. Vehicle, adapted for communication with a node of a system (100), comprising: a communication network of interconnected and cooperating nodes (10) and a central control station (200), each node being capable of communicating to at least one adjacent node and/or to the central control station, each node comprising: at least one microphone (11) arranged for receiving outdoor sound; location means (12) providing information regarding its location; clock means (13) providing time information; a processing circuit (17), capable of processing the output signals of the corresponding microphone (11), the processing circuit (17) being designed to detect the occurrence of predetermined characteristic sound patterns, and if the occurrence of a predetermined characteristic sound pattern is detected, to communicate the detected event to the central station (200), together with information regarding location of the node and time of detection; wherein the clock means (13) of all nodes are accurately synchronised; and wherein the central station (200) is designed to process the information received from a plurality of nodes and to determine the location of the event and the occurrence time of the event, comprising a control device adapted to automatically switch ON or OFF apparatus like heating equipment, airconditioning equipment, windscreen wipers, etc. in response to receiving weather information from a node of a system of claim
 17. 25. Vehicle according to claim 23, comprising one or more weather sensors, adapted to communicate readings of its weather sensors to a node (10). 